import pandas as pd
import numpy as np

b = pd.Series([1,2,3,4],index = ['a','b','c','d'])
c = pd.Series([1,2,3,4],index = ['c','d','a','b'])
d = pd.Series([1,2,3,4,8],index = ['c','d','a','b', 'e'])

print(b + c)
print(b + d)
print(b.add(d, fill_value=0))
